We propose to study the regulation of somatic sexual development in D. melanogaster by combined molecular and genetic studies of sex determination loci and the genes they control. Sequences expressed sex-specifically inlarvae, pupae or adults will be identified by differential hybridization to cDNAs made from polyA+ RNAs of female or male animals. Transcripts whose abundance in poly A+ RNA is affected by mutations at sex determination loci will be selected for further study. Expression of the sex-specific transcripts will be compared quantitatively and qualitatively in wild type and sex determination mutants. These studies, to be done with null mutants as well as with temperature shifts of tra2ts homozygotes, will establish the molecular level and generality of control by the regulatory loci. They will also extend, beyond genetically-determined limits, knowledge of the development times and tissues in which the regulatory loci act to control sex-specific gene expression. DNA and chromatin organization of the sex-specific genes will be compared to determine features important for sex-specific control. Assignment of regions important for this control will be tested by in vitro alteration of putative control regions, introduction of these derivatives into flies, and observation of the sex-specificity of expression of transcribed sequences in the constructs. Mutants in genes encoding sex-specific transcripts of interest will be isolated using the sequences' chromosomal location and characteristics of expression as guides. The mutants will be useful in testing the above findings genetically as well as in determining the in vivo function of their genes. Genetic studies of mutations defining new regulatory genes will establish their relation to other sex determination loci, and the tissue-specificity of their expression. These, and molecular studies of the effects of the new loci on the expression of the genes they regulate, will expand knowledge of the regulatory hierarchy governing sexual phenotype.